Introduction
An X-Wing aircraft is a rotary wing aircraft that uses a rigid rotor/wing utilizing circulation control airfoils. The rotor is driven mechanically, and the rotor may rotate, as in a helicopter, or it may be stopped and positioned so as to act like a fixed wing.
Collective and cyclic control is achieved by control of air flowing around a Coanda surface on the blade airfoils. This is done by blowing compressed air through leading edge and trailing edge ducts in the rotor blades and modulating the amount of air being ejected through span-wise slots on the leading and trailing edges of the rotor blades.
The rotor system for an X-Wing aircraft includes a hub and attached rotor blades and a pneumatic system for delivering pressurized air separately to the leading edge and the trailing edge of the individual rotor blades at a desired pressure and mass flow. The pneumatic system includes a compressor, a stationary air supply chamber, valving for controlling the flow of air from the chamber to the blades, and a rotating air distribution arrangement for conducting air separately to the leading edge and trailing edge of the blades.
In circulation control airfoils, pressurized air is ejected from span-wise openings or slots along the upper side of the rounded airfoil leading/trailing edge Coanda surface. The airflow from the slots attaches to the rounded leading/trailing edge, which increases the circulation, to provide a corresponding lift increase over an airfoil having no ejected air. For a given blade internal pressure and aerodynamic condition, the lift change due to circulation control is proportional to the area of the slot opening up to a certain limit. When the slot opening exceeds this limit, no additional lift is achieved, a condition analogous to a stall in a conventional airfoil.
Since an X-Wing circulation control airfoil is symmetrical about its half chord, the leading edge on the advancing side of the blade path disk becomes the trailing edge on the retreating side, and vice-versa. To maximize performance as the rotor slows down, it is desirable that the "local" leading edge slot be closed at all azimuth positions.
Conventional helicopters provide aircraft pitch and roll control by varying blade pitch from medium-to-high, or medium-to-low to medium at a once "per rev" (rotor revolution) rate, as the blades whirl around the rotor disk. The X-Wing aircraft includes 1-per-rev pneumodynamic control and also has more rapid pneumatic variance, at an up to 5-per-rev rate, to system loads and vibrations.
It achieves rotor control via a pneumatic medium. It is a full authority fly-by-wire (FBW) system with, for example, quadruple redundancy for all flight critical functions.
The X-Wing aircraft is designed to hover like a helicopter and cruise at an airplane's high speeds. It uses a stoppable rotor/wing, which, as noted, rotates like a helicopter rotor in low speed flight and stops to become a fixed wing for high speed cruise. It offers an ideal compromise for VTOL hover/cruise capabilities, horsepower/fuel efficiency and ultimate payload capacity.
Some exemplary X-Wing related patents, all owned by the assignee hereof, are listed below:
______________________________________ Patent No. Patentee(s) Issue Date Title ______________________________________ 4,493,612 D'Anna 01/15/85 "Axially Slideable Plenum for Circulation Control Aircraft" 4,507,050 Jeffery et al 03/26/85 "Pneumatic Valve Control for Circulation Control Aircraft" 4,534,702 Johnson et al 08/13/85 "Pneumatic Control Valve Actuator Computer Control Arrangement" 4,573,871 Krauss et al 03/04/86 "X-Wing Aircraft Circulation Control" 4,583,704 Krauss et al 04/22/86 "Pneumatic System Structure for Circulation Control Aircraft" 4,594,537 Arifian et al 06/10/86 "Redundant Control System for X-Wing Value Actuators" 4,596,512 Krauss 06/24/512 "Circulation Controlled Rotor Blade Tip Vent Value" 4,626,171 Carter et al 12/02/86 "Rotor Blade Construction for Circulation Control Aircraft" 4,678,401 Bradford et at 07/07/87 "Rotor Control System" ______________________________________
A revolutionary concept such as "X-Wing" requires innovative approaches to service the technology leap involved in this type of hybrid aircraft.
The control laws are one area of such a vehicle which face significant challenges. The control law system must first be designed to accommodate the equivalent of three vehicles, since the X-Wing operates in a rotary wing mode (RW), a fixed wing or stopped rotor mode (SR), and a conversion state (CV) between the two.
For purposes of this disclosure, it should be understood that the phrase "flight mode" refers to the state of the rotor, including its stopped rotor mode (SR), its rotary wing mode (RW) and the conversion state (CV), while "flight condition" refers to aircraft air speed and the angle of attack (AOA). In turn, "flight situation" refers to both rotor mode and aircraft condition.